New York: In a major breakthrough, scientists have designed nanoparticles that can deliver drugs directly to a tumor.

But what makes it special is that those nanoparticles that do not hit their target can be broken down and eliminated easily.

The nanoparticle is encased in a shell coated with a peptide that enables it to target tumor cells.

"The disassembly is an interesting concept for creating drugs that respond to a certain stimulus," said Gary Braun, a post-doctoral associate in the Ruoslahti Lab at University of California, Santa Barbara.

It also minimises the off-target toxicity by breaking down the excess nanoparticles so that they can then be cleared through the kidneys, he added.

The method for removing nanoparticles unable to penetrate target cells is unique.

"By focusing on the nanoparticles that actually got into cells, we can then understand which cells were targeted and study the tissue transport pathways in more detail," Braun explained.

Some drugs are able to pass through the cell membrane on their own, but many drugs, especially RNA and DNA genetic drugs, are charged molecules that are blocked by the membrane.

These drugs must be taken in through endocytosis, the process by which cells absorb molecules by engulfing them.

"This typically requires a nanoparticle carrier to protect the drug and carry it into the cell," Braun noted.

"And that is what we measured - the internalisation of a carrier via endocytosis," he said.

Because the nanoparticle has a core shell structure, the researchers can vary its exterior coating and compare the efficiency of tumor targeting and internalisation.